For many processes, an exiting stream, whether considered a waste stream, a by-product, or the main desired stream, is composed of a solid material wet with water. This water is typically found in both the interstitial spaces of the solid and is absorbed or adsorbed by the solid. Water such as this has typically been removed by drying the solids with thermal energy. This process generally requires a large amount of heat or energy to remove the water from the solids and obtain dry, usable solids.
Attempts have been made to use organic solvents to remove water from wet solids using solvents such as hexane. Essentially, the hexane is used to displace the water from the solids. The hexane remaining with the solids is then evaporated from the solids with thermal energy. Again, this process generally requires a large amount of thermal energy, but less than if water alone was being dried from the solids. However hexane also brings with it certain other concerns, such as toxicity. Further, because of poor displacement, large amounts of residual water may remain with the solids.
Some examples of known extraction methods include Baird, U.S. Pat. No. 4,251,231, which utilizes liquid-liquid extraction to directly extract alcohol suitable for use in gasohol from a fermentation mixture. Gasoline was used as the extraction solvent. The water was removed by either the use of adsorbents or absorbents, or by chilling the extracted alcohol-gasoline product to a temperature below about −10° F., thereby removing the water.
During the ethanol manufacturing process, solids, wet with primarily water and some ethanol, exit the fermentation process as a beer stream. Other materials, such as oils and glycerol are also present in the beer stream. It is desired to obtain individual output streams of dry solids, water, and ethanol.
The beer stream solids, as discussed above, have the water in both the interstitial spaces of the solid and that which is absorbed or adsorbed by the solid. This water, and any ethanol, has typically been removed by drying the solids with thermal energy. Preferably, the ethanol is recovered and is used; unfortunately, recovery of pure, or fairly pure ethanol, is not usual. Additionally, preferably the water is sufficiently pure that the water can be readily disposed; unfortunately, the water has contaminants that inhibit direct, unmanaged disposal. Still further, contaminants, such as oils and glycerol, remain in the solids, making them undesirable for many applications.
What is needed is a low cost, more heat or energy efficient process for drying solids wet with water. It would be beneficial if the various output streams from the process could be reclaimed and used.